A week after Stephen K. Bannon helped engineer the populist revolt that led to Donald J. Trump’s election, Buzzfeed unearthed a recording of him speaking to a Vatican conference of conservative Catholics in 2014.

In his presentation, Mr. Bannon, then the head of the hard-right website Breitbart News and now Mr. Trump’s chief strategist, called on the “church militant” to fight a global war against a “new barbarity” of “Islamic fascism” and international financial elites, with 2,500 years of Western civilization at risk.

While most listeners probably overlooked the term “church militant,” knowledgeable Catholics would have recognized it as a concept deeply embedded in the church’s teaching. Moreover, they would have noticed that Mr. Bannon had taken the term out of context, invoking it in a call for cultural and military conflict rather than for spiritual warfare, particularly within one’s soul, its longstanding connotation.

As the Trump administration prepares to take office, the use of Church Militant theology has gone well beyond its religious meaning and has taken on a political resonance. To fully grasp what “church militant” means in this highly politicized atmosphere, it helps to examine the broader movement and the role of a traditionalist Catholic website called — to no surprise — ChurchMilitant.com.

The site’s right-wing stances against globalism, immigration, social-welfare programs and abortion, as well as its depiction of an existential war against radical Islam, mesh with many of the positions espoused by Mr. Trump and his inner circle. (Mr. Bannon did not respond to questions submitted to the Trump transition office.)

Michael Voris, the senior executive producer of ChurchMilitant.com, said the website’s positions were a righteous defense of patriotism and morality on behalf of people who believe those virtues have been attacked by liberals, secularists and global elites.

“This is breaking down into forces that believe in God and those that don’t,” he said, adding, “Largely, I would say this is a war of religion versus nonreligion.”

For some Catholic scholars and anti-hate advocates, the emergence of Church Militant theology in a politicized and highly partisan way is disturbing.

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A chapel in the offices of ChurchMilitant.com in Ferndale, Mich.CreditBrittany Greeson for The New York Times

“This is a hard-core group, and the question is whether the number is growing,” said the Rev. John T. Pawlikowski, a professor of social ethics at the Catholic Theological Union in Chicago, referring to the broader movement that includes ChurchMilitant.com. “If the Trump election baptizes this stuff as more authentic Catholic teaching, that would be a disaster.”

The term has roots in the early centuries of the church, when the Catholic community — living and dead — was envisioned as having three parts. These were later called the Church Triumphant (composed of those in heaven), the Church Suffering or Church Penitent (those in purgatory) and the Church Militant (those on earth).

Catholic teaching held that the spiritual efforts of the Church Militant would hasten the ascent into heaven of the souls in purgatory. But how is a concept that was formed during Roman persecution of early Christians and took on a martial connotation during the Crusades meant to be understood in a democratic, capitalist, polyglot, multimedia society like the modern United States?

“When you heard the expression ‘the Church Militant,’ it didn’t bring to mind a call to arms or some kind of mobilized, militant action in the way we understand the term now,” said John C. Cavadini, a professor of theology at the University of Notre Dame. “A lot of the struggle of the Church Militant is against interior temptations that lead you to greed and all kinds of spiritual pathologies. And it’s about engaging in acts of mercy. Part of the victory of the Church Militant is the victory of love. It didn’t have the triumphalist and militarized connotation that’s been attached to it now.”

While the term remains in the Roman catechism, which was promulgated by the Council of Trent in the mid-1500s, the official catechism produced under Pope John Paul II in 1992 replaced “Church Militant” with “pilgrims on earth.” The adult catechism then devised by Catholic bishops in the United States adopted those words, and they are overwhelmingly the norm in Catholic practice in the United States and abroad.

Patrick J. Buchanan, one of Mr. Trump’s precursors in running for president on a platform of right-wing populism, embraced Church Militant theology in a 2009 essay in the conservative magazine Human Events. After delineating conflicts between Catholic leaders and Democratic politicians over issues like abortion and contraception, Mr. Buchanan made a more sweeping assertion:

“Catholicism is necessarily an adversary faith and culture in an America where a triumphant secularism has captured the heights, from Hollywood to the media, the arts and the academy, and relishes nothing more than insults to and blasphemous mockery of the Church of Rome.”

The words could serve as a mission statement for Mr. Vorsi’s ChurchMilitant.com. A television producer who renounced his earlier life as a gay man, Mr. Voris, 55, has developed a media operation from ChurchMilitant.com’s studio in suburban Detroit that produces books, online articles, YouTube videos, podcasts and a daily talk show. These cumulatively attract about 1.5 million views a month, he said.

In an earlier iteration, ChurchMilitant.com operated as Real Catholic TV, until the Archdiocese of Detroit forced it to stop using the name because it had no permission. While some of the core issues for ChurchMilitant.com are staples of traditionalist Catholics — advocating the Latin Mass, for instance — others map neatly onto the secular political landscape. And they do so in a highly strident way.

ChurchMilitant.com, for example, has dismissed climate change as a hoax. It likened the Black Lives Matter movement to “the new fascism.” Hillary Clinton, whom it routinely calls “Killary,” was “Satan’s mop for wiping up the last remaining resistance to him in America.” Mr. Voris has described social-welfare programs as a system in which “half the people of America” pay no taxes and “get things handed to them.”

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In the offices of ChurchMilitant.com. The site has dismissed climate change as a hoax, likened the Black Lives Matter movement to the “new fascism” and referred to Hillary Clinton as “Killary.”CreditBrittany Greeson for The New York Times

Contrary to the Second Vatican Council’s endorsement of interreligious dialogue, Mr. Voris views Islam as “entirely different” from Christianity and portrays Judaism in outdated terminology that experts in Catholic-Jewish relations consider anti-Semitic. (The Trump campaign was accused at times of indulging in and even disseminating anti-Jewish rhetoric and imagery.)

In a statement that echoed one made by Mr. Bannon when he was still with Breitbart, Mr. Voris maintained that American Catholic bishops supported immigration solely to “shore up flagging numbers of Catholics” and rebuild a “shrinking, shriveling church” with both legal and illegal arrivals from Mexico.

More broadly, Mr. Voris blames Cardinal Joseph Bernardin, the archbishop of Chicago who died in 1996, for his “seamless garment” theology, which united such stances as opposition to abortion, euthanasia, nuclear arms and the death penalty under a “consistent ethic of life.” To Mr. Voris, that formulation is “a total whitewash of Catholic social teaching.”

Not all of Mr. Voris’s criticisms are aimed at Catholics. He has also singled out the liberal philanthropist George Soros and the deceased community organizer Saul Alinsky, familiar targets for conservative activists like Newt Gingrich and Glenn Beck. Mr. Voris, though, goes a significant step further by prominently identifying both Mr. Soros and Mr. Alinsky as Jewish.

Why is their religion relevant, particularly as neither man was observant? Mr. Voris responded, “The fuel, as it were, for the Democratic Party has come from a liberal Jewish mind-set.”

Such a comment might not sound so offensive were it not for Mr. Voris’s overarching views of Jews, which contravene Catholic policy since the Second Vatican Council. In a 2010 episode of ChurchMilitant.com’s webcast “The Vortex,” he contended that the Roman destruction of the Second Temple ended God’s covenant with the Jews. Subsequent Judaism, he said, is merely a “man-made religion.”

Asked about the statements, Mr. Voris said: “I’m not anti-Semitic at all. I’m just speaking on theological grounds.”

The explanation did not impress Mark Weitzman, an expert in hate groups for the Simon Wiesenthal Center, who has studied ChurchMilitant.com. “What he says about Jews is classical supersessionist anti-Semitism,” Mr. Weitzman said, “and if he doesn’t repudiate it, that’s a problem.”

Repudiation does not appear likely for any of ChurchMilitant.com’s extremist positions, especially now that kindred spirits are about to take control of the executive branch of the American government.

“The Trump election gave permission to a lot of people who would never say certain things publicly to say them,” said the Rev. Mark S. Massa, a professor of church history at Boston College. “And for those who have been saying them all along, the repercussions will be minimal.”

A version of this article appears in print on , on Page A12 of the New York edition with the headline: ‘Church Militant’ Theology Is Put to New, and Politicized, Use. Order Reprints | Today’s Paper | Subscribe